1. Field of the Invention
The present invention relates to an optical pickup device and a recording and reproducing apparatus, and more particularly to an optical pickup device, and a recording and reproducing apparatus compatible with a recording medium for recording information by multi-photon absorption.
2. Description of the Related Art
Conventionally, there has been used a material (a phase change material, a pigment material, and the like) having a property that the refractive index of a recording layer is changed by absorbing one photon, as a recording layer material. In recent years, there has been proposed a recording medium using a so-called two-photon absorbing material having a property that the refractive index of a recording layer is changed by absorbing two photons, as a recording layer material. In addition to the above, there is an idea of using a multi-photon absorbing material having a property that the refractive index of a recording layer is changed by absorbing three or more photons, as a recording layer material.
In the case where a two-photon absorbing material is used as a recording layer material, information is recorded by two-photon absorption. The two-photon absorption is a phenomenon that a material is excited by absorbing two photons. The probability of occurrence of two-photon absorption is proportional to the square of an incident light intensity (non-linear optical effect). In other words, two-photon absorption is induced solely in an area where the energy of incident light is concentrated. Condensing incident light through a lens enables to generate a condition that two-photon absorption occurs solely on a focal point including its vicinity, whereas two-photon absorption does not occur in the other space where light is not focused. Specifically, two-photon absorption can be induced in the two-photon absorbing material by condensing and irradiating laser light having an absorption wavelength bandwidth of the two-photon absorbing material with an ultra-short pulse and a high intensity. There is also proposed a method for inducing two-photon absorption in a two-photon absorbing material by condensing and irradiating laser light having an absorption wavelength bandwidth of the two-photon absorbing material, while irradiating light of a wavelength other than the absorption wavelength bandwidth. In the latter method, the energy level of the two-photon absorbing material is raised by the light of the wavelength other than the absorption wavelength bandwidth. Accordingly, two-photon absorption is induced even if the intensity level of laser light having the absorption wavelength bandwidth is suppressed to some extent.
An optical recording medium of the above kind may have, for example, an arrangement that a plurality of recording layers and one servo layer are laminated. In the recording medium, a plurality of flat recording layers without guide tracks are formed, and a servo layer having a guide track is formed on these recording layers.
In this arrangement, in performing a recording operation, a focusing servo signal and a tracking servo signal are generated based on the guide track formed in the servo layer, and recording laser light and reproducing laser light are positioned on a recording layer based on the servo signals. Accordingly, the recording laser light and the reproducing laser light scan the recording layer to follow an intended scanning trajectory, whereby information is recorded/reproduced with respect to the recording layer.
In the case where a recording operation is performed with respect to an optical recording medium using a multi-photon absorbing material, similarly to an existing optical disc, it is necessary to adjust the power of recording laser light to a proper level. If the power of recording laser light is unduly small, information cannot be smoothly recorded. If, on the other hand, the power of recording laser light is unduly large, problems such as erroneous recording in an adjacent track, or cross-erasing may occur.
In an existing optical disc apparatus, a test-recording operation is performed with respect to a test-write area with a different power, and an optimal recording power with respect to an optical disc to be recorded is set, based on a data error ratio or the like to be obtained in reproducing from the test-write area. In this arrangement, however, since two steps i.e. a test-writing step and a reproducing step are necessary, there is a problem that a certain time is required for setting a recording power.